7,979 research outputs found
Planes of satellite galaxies and the cosmic web
Recent observational studies have demonstrated that the majority of satellite
galaxies tend to orbit their hosts on highly flattened, vast, possibly
co-rotating planes. Two nearly parallel planes of satellites have been
confirmed around the M31 galaxy and around the Centaurus A galaxy, while the
Milky Way also sports a plane of satellites. It has been argued that such an
alignment of satellites on vast planes is unexpected in the standard
({\Lambda}CDM) model of cosmology if not even in contradiction to its generic
predictions. Guided by {\Lambda}CDM numerical simulations, which suggest that
satellites are channeled towards hosts along the axis of the slowest collapse
as dictated by the ambient velocity shear tensor, we re-examine the planes of
local satellites systems within the framework of the local shear tensor derived
from the Cosmicflows-2 dataset. The analysis reveals that the Local Group and
Centaurus A reside in a filament stretched by the Virgo cluster and compressed
by the expansion of the Local Void. Four out of five thin planes of satellite
galaxies are indeed closely aligned with the axis of compression induced by the
Local Void. Being the less massive system, the moderate misalignment of the
Milky Way's satellite plane can likely be ascribed to its greater
susceptibility to tidal torques, as suggested by numerical simulations. The
alignment of satellite systems in the local universe with the ambient shear
field is thus in general agreement with predictions of the {\Lambda}CDM model.Comment: 9 pages, 3 figures, 3 tables. Accepted by MNRAS, 9 June 201
Critical conditions for the wetting of soils
The wettability of soil is of great importance for plants and soil biota and in determining whether flooding and soil erosion will occur. The analysis used in common measurements of soil hydrophobicity makes the assumption that water always enters soils if the average contact angle between the soil and water is 90 degrees or lower; these tests have been used for decades. The authors show theoretically and experimentally that water cannot enter many soils unless the contact angle is considerably lower than this, down to approximately 50 degrees. This difference generates serious errors in determining and modeling soil wetting behavior
Surface-induced heating of cold polar molecules
We study the rotational and vibrational heating of diatomic molecules placed
near a surface at finite temperature on the basis of macroscopic quantum
electrodynamics. The internal molecular evolution is governed by transition
rates that depend on both temperature and position. Analytical and numerical
methods are used to investigate the heating of several relevant molecules near
various surfaces. We determine the critical distances at which the surface
itself becomes the dominant source of heating and we investigate the transition
between the long-range and short-range behaviour of the heating rates. A simple
formula is presented that can be used to estimate the surface-induced heating
rates of other molecules of interest. We also consider how the heating depends
on the thickness and composition of the surface.Comment: 17 pages, 7 figure
Enhancing socio-emotional communication and quality of life in young cochlear implant recipients: Perspectives from parameter-specific morphing and caricaturing
The use of digitally modified stimuli with enhanced diagnostic information to improve verbal communication in children with sensory or central handicaps was pioneered by Tallal and colleagues in 1996, who targeted speech comprehension in language-learning impaired children. Today, researchers are aware that successful communication cannot be reduced to linguistic information—it depends strongly on the quality of communication, including non-verbal socio-emotional communication. In children with cochlear implants (CIs), quality of life (QoL) is affected, but this can be related to the ability to recognize emotions in a voice rather than speech comprehension alone. In this manuscript, we describe a family of new methods, termed parameter-specific facial and vocal morphing . We propose that these provide novel perspectives for assessing sensory determinants of human communication, but also for enhancing socio-emotional communication and QoL in the context of sensory handicaps, via training with digitally enhanced, caricatured stimuli. Based on promising initial results with various target groups including people with age-related macular degeneration, people with low abilities to recognize faces, older people, and adult CI users, we discuss chances and challenges for perceptual training interventions for young CI users based on enhanced auditory stimuli, as well as perspectives for CI sound processing technology
Molecular motor traffic in a half-open tube
The traffic of molecular motors which interact through mutual exclusion is
studied theoretically for half-open tube-like compartments. These half-open
tubes mimic the shapes of axons. The mutual exclusion leads to traffic jams or
density plateaus on the filaments. A phase transition is obtained when the
motor velocity changes sign. We identify the relevant length scales and
characterize the jamming behavior using both analytical approximations and
Monte Carlo simulations of lattice models.Comment: 14 pages, 5 postscript figure
Hermitian Young Operators
Starting from conventional Young operators we construct Hermitian operators
which project orthogonally onto irreducible representations of the (special)
unitary group.Comment: 15 page
The alignment of galaxy spin with the shear field in observations
Tidal torque theory suggests that galaxies gain angular momentum in the
linear stage of structure formation. Such a theory predicts alignments between
the spin of haloes and tidal shear field. However, non-linear evolution and
angular momentum acquisition may alter this prediction significantly. In this
paper, we use a reconstruction of the cosmic shear field from observed peculiar
velocities combined with spin axes extracted from galaxies within () from 2MRS
catalog, to test whether or not galaxies appear aligned with principal axes of
shear field. Although linear reconstructions of the tidal field have looked at
similar issues, this is the first such study to examine galaxy alignments with
velocity-shear field. Ellipticals in the 2MRS sample, show a statistically
significant alignment with two of the principal axes of the shear field. In
general, elliptical galaxies have their short axis aligned with the axis of
greatest compression and perpendicular to the axis of slowest compression.
Spiral galaxies show no signal. Such an alignment is significantly strengthened
when considering only those galaxies that are used in velocity field
reconstruction. When examining such a subsample, a weak alignment with the axis
of greatest compression emerges for spiral galaxies as well. This result
indicates that although velocity field reconstructions still rely on fairly
noisy and sparse data, the underlying alignment with shear field is strong
enough to be visible even when small numbers of galaxies are considered -
especially if those galaxies are used as constraints in the reconstruction.Comment: 9 pages, 3 figures, accepted in MNRA
Generalizing Tsirelson's bound on Bell inequalities using a min-max principle
Bounds on the norm of quantum operators associated with classical Bell-type
inequalities can be derived from their maximal eigenvalues. This quantitative
method enables detailed predictions of the maximal violations of Bell-type
inequalities.Comment: 4 pages, 2 figures, RevTeX4, replaced with published versio
Elastic-Net Regularization: Error estimates and Active Set Methods
This paper investigates theoretical properties and efficient numerical
algorithms for the so-called elastic-net regularization originating from
statistics, which enforces simultaneously l^1 and l^2 regularization. The
stability of the minimizer and its consistency are studied, and convergence
rates for both a priori and a posteriori parameter choice rules are
established. Two iterative numerical algorithms of active set type are
proposed, and their convergence properties are discussed. Numerical results are
presented to illustrate the features of the functional and algorithms
Spectroscopy of Ne for the thermonuclear O()Ne and F()O reaction rates
Uncertainties in the thermonuclear rates of the
O()Ne and F()O reactions
affect model predictions of light curves from type I X-ray bursts and the
amount of the observable radioisotope F produced in classical novae,
respectively. To address these uncertainties, we have studied the nuclear
structure of Ne over MeV and MeV using
the F(He,t)Ne reaction. We find the values of the
4.14 and 4.20 MeV levels to be consistent with and
respectively, in contrast to previous assumptions. We confirm the recently
observed triplet of states around 6.4 MeV, and find evidence that the state at
6.29 MeV, just below the proton threshold, is either broad or a doublet. Our
data also suggest that predicted but yet unobserved levels may exist near the
6.86 MeV state. Higher resolution experiments are urgently needed to further
clarify the structure of Ne around the proton threshold before a
reliable F()O rate for nova models can be determined.Comment: 5 pages, 3 figures, Phys. Rev. C (in press
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